Spark plug



V. R. THOMAS Nov. 4, 1952 SPARK PLUG Filed Oct. 22. 1949 Patented Nov. 4, 1952 UNITED STATES PATENT OFFICE SPARK PLUG Vernon R. Thomas, Rockford, Ill.

Application October 22, 1949, Serial N0. 123,033

(Cl. 12S-169) 3 Claims.

This invention relates to spark plugs of the type in which the center electrode is enclosed in a metallic dome dening an auxiliary ignition chamber which is apertured to permit the entry of the combustible mixture and rapid outward propagation of the flame after ignition.

One object of the present invention is to provide a spark plug ofthe above character having a gap which is adjustable in a novel manner from the exterior of the plug without destroying the Vgas tight seal between the relatively moving parts.

Another object is to construct the seal between the relatively adjustable parts in a novel manner which permits the operating temperature of the plug to be controlled.

Other objects and advantages of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings, in which Figure 1 is an elevational view of a spark plug embodying the novel features of the present invention.

Fig. 2 is a section taken along the line 2-2 of Fig. 1.

Fig. 3 is a sectional view taken along the line 3-3 of Fig. 2.

WhileV the invention is susceptible of various modications and alternative constructions, I have shown in the drawings and will herein describe in detail the preferred embodiment. It is to be understood, however, that I do not intend to limit the invention by such disclosure but aim to cover all modifications and alternative constructions falling within the spirt and scope of the invention as expressed in the appended claims.

The improved spark plug is similar in general construction to the plugs commonly used in internal combustion engines including a cylindrical metallic shell I8 having an upper portion usually of hexagonal cross section and a lower portion of reduced diameter externally threaded at II to screw into an opening in the cylinder head of an engine. The center electrode comprises a round rod I2 extending through atube I3 of hard ceramic material having an external flange I4 seated against an internal shoulder I5 in the shell I0 and clamped against the latter by a screw plug I6.

The inner gradually tapering end portion I'! of the ceramic tube is enclosed by the threaded part of the shell i and by a frusto conical dome I8 integral therewith and having a plurality, four in the present instance, of angularly spaced holes i I9 of about .110 of an inch in diameter extending diagonally through the cone. The end of the dome I8 is flat and preferably formed at its center with a hole 20 about .D78 of an inch in diameter. The shell I0, the dome I8, and the tapered end II of the tube cooperate to dene an auxiliary combustion chamber 2| around the end 22 of the center electrode I2 which end faces toward and is disposed parallel to the inner at surface 23 of the dome I8 with which the electrode cooperates to define a spark gap of the desired width. A large sparking area is thus provided so as to insure proper combustion of the gas within the chamber 2l followed by rapid propagation of the resulting flame outwardly through the holes I9 and 29 in a plurality of jet-like streams. Very eiiicient ignition of the main mass of combustible gas in the engine cylinder is thus achieved.

Provision is made for adjusting the center electrode I2 axially by means of a tool engaging the electrode at a point exteriorly of the plug. For this purpose, the outer half portion of the rod I2 is larger than the electrode end and is threaded into an elongated nut 24 cemented tightly into a cylindrical counterbore 25 in the ceramic tube A slot 2B or other tool receiving recess is` I3. formed in the outer end of the screw to enable the rod to be turned within the nut and the electrode end 22 to be advanced toward or away from the surface 23 of the grounded electrode.

The smooth inner end portion of the electrode rod I2 extends loosely through a bore 21 in the ceramic tube and, in accordance with the present invention, a seal 28 of novel construction is provided between the exterior of the rod I2 and the wall of the counterbore 25. For this purpose, the counterbore is extended beyond the inner end of the nut 24, and the cylindrical space thus formed is filled with loose granular or fibrous material which may be compressed or packed tightly into a tubular body which seals the tube I3 against the escape of gas under pressure along the surface of the rod I2 with-out at the same time preventing subsequent free turning of the rod as `required in order to readjust the width of the spark gap. Preferably, heat insulating material such as ordinary rock wool is employed, although various other well known inorganic fibrous materials including glass wool, asbestos, etc. having comparable properties may be employed.

To form the seal 28, the tube I3 is assembled in the shell IIJ and, before insertion of the center electrode I2, loose heat insulating material such as rock wool is placed in the counterbore and compressed against the inner end thereof under a pressure of approximately 1000 pounds per square inch. The amount of the material thus packed into the tube is suicie-nt to impart the desired length to the seal 28. Then the nut 24 is screwed onto the rod I2 and coated on its exterior with ordinary spark plug cement. This assembly is then pressed axially into the tube forcing the smaller electrode end of the rod down through the packed insulating material until the outer end of the nut becomes flush with the end of the tube I3. The cement is set by baking the resulting assembly.

By employing heat insulating material and properly locating the latter in relation to the flange Ill of the ceramic tube, the seal 28 may be utilized to perform the additional function of increasing to the desired point the temperature which the active parts of the plug attain in service use. Such high temperature operation is desirable in certain engines using heavy fuel and relatively low compression ratios. Thus, by extending the counterbore inwardly along the tube I3 a substantial distance beyond the screw plug I6 and Well into the metallic shell I0, the effective cross-sectional area of the ceramic tube through which heat may be conducted to the metal of the shell it is reduced correspondingly and the temperature attained at the electrode Surface is raised proportionately. The precise operati-ng temperature may be varied as desired by extending or shortening the counterbore and therefore changing the location of the insulating seal 23. Thus, if the inner end of the bore is extended farther toward the electrode surfaces 22 and 23, a higher operating temperature will obtain while by shortening the bore, the section of the ceramic available for the conduction of heat to the metal of the shell I8 will be increased and the operating temperature of the plug will be lowered by virtue of the more rapid rate of heat conduction through the ceramic and to the shell.

By `packing loose material into the counterbore to form the seal 28, the necessity of using ordinary spark plug cement or other such material to avoid the escape of combustible gas along the center electrode is avoided. There is, therefore, no `adherence between the seal and the rod I2 so that the latter is quite free and may be turned within the nut 2Q to advance the end surface 22 and thus reduce the width of the y spark gap. The seal material being compressible does not interfere materially with the advance of the inner end of the screw which is somewhat larger than the electrode portion of the rod I2. It is preferred to use rock wool to form the seal 23 since this particular type of heat insulating material is not resilient and remains compressed after it is packed tightly so as to retain an effective seal around the rod I2 following initial adjustment of the latter and further adjustments after service use.

To increase the effectiveness of the seal in preventing the escape of gases outwardly through the tube, a gasket 29, preferably co-mprising a washer of soft metal such as a lead-antimony alloy, fits snugly around the screw and is compressed tightly against the outer end of the ceramic tube by means of a nut 30. A cap 3I threaded onto the outer end of the screw provides a suitable terminal for attachment of the ungrounded conductor to the plug.

I claim as my invention:

1. A spark plug comprising an elongated tube of insulation having an axial cylindrical bore extending through one end portion thereof and a counterbore extending through the remaining portion of the tube, a nut rigid with said tube and projecting into the open end of the counterbore short of the inner end of the latter, an elongated metal electrode rod extending axially through said tube and having one end portion threaded into said nut and the other end portion extending through said bore beyond the outer end of the latter, the portion of said rod between the thread thereon and the inner end of said counterbore having a smooth external surface, a hollow metallic shell rigidly supporting said tube and surrounding said rst end portion thereof with the inner end of said counterbore located intermediate the ends of the shell, an electrode on said shell cooperating with the projecting end of said rod to define a spark gap, and means providing a gas-tight seal between said rod and said tube permitting turning of the rod and advance of the latter axially through the tube, said means comprising a body of loose compressible heat insulating material packed tightly in said counterbore around said smooth surface to reduce the rate of heat conduction between said rod and said shell, said packed body extending between and abutting at opposite ends against the inner ends of said nut and counterbore.

2. A spark plug comprising a hollow metallic shell having an internal axially facing shoulder, a tube of insulation projecting through said shell and having an external flange intermediate its ends seated rigidly against said shoulder, said tube having a counterbore extending from one end of the tube toward said shoulder and terminating at a point adjacent but axially spaced from the shoulder, a nut secured in the outer end portion of said counterbore with its inner end axially spaced short of the end of the counterbore, an elongated metallic electrode rod having one end portion threaded into said nut and extending axially through said counterbore and an axial bore in the other end portion of the tube and beyond the other tube end, the portion of said rod between the thread thereon and the inner end of said counterbore having a smooth external surface, an electrode on said shell cooperating with the projecting end of said rod to denne a spark gap, and means providing a gastight seal between said rod and said tube permitting turning of the rod and advance of the latter axially through the tube, said means comprising a body of loose heat insulating material compressed tightly within said counterbore and around the length of said smooth rod surface between said nut end and the inner end of said counterbore to reduce the rate of heat conduction between said rod and said shell.

3. A spark plug comprising an elongated tube of insulation having an axial cylindrical bore extending through one end portion thereof and an axial counterbore extending through the other end portion to a point within said first end portion and having a generally cylindrical inner end, a nut rigid with said tube and extending into the open end of said counterbore with its inner end spaced a substantial distance short of the inner end of the latter, an elongated metal electrode rod extending axially through said tube and having one end portion threaded into said nut and the other end portion extending through said bore beyond the outer end of the latter, the portion of said rod within said counterbore beyond the inner end of said thread having a smooth external cylindrical surface, a hollow metallic shell rigidly supporting said tube and surrounding said flrst end portion thereof With the inner end of said counterbore located within the shell, an electrode on said shell cooperating with said other end of said rod to dene a spark gap, and means providing a gas-tight seal between said rod and said tube permitting turning of the rod and advance of the latter axially through the tube, said means comprising a body of rock Wool tightly packed in the inner end portion of said counterbore around a length of said smooth rod surface to reduce the conduction of heat away from said rod to said shell through said tube, said packed rock Wool lling the space between the inner ends of said nut and counterbore.

VERNON R. THOMAS.

6 REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,360,294 Hill Nov. 30, 1920 1,384,914 Orsinger July 19, 1921 1,776,449 Powell Sept. 23, 1930 2,110,652 Nowosielski Mar. 8, 1938 2,195,543 Songer Apr. 2 ,1940

FOREIGN PATENTS Number Country Date 220,207 Great Britain Aug. 14, 1924 354.279 Great Britain Jan. 29, 1930 

